1. Technical Field
The present invention relates generally to removing oil and water from sand, for example, to clean up oil spills, sludge pits, and oil well cuttings. The present invention more particularly relates to a continuous process for separating oil, water and sand that has a high through-put and does not involve incineration or discharge of cleaning agents. Specifically, the present invention relates to a continuous process that separates oil and water from sand and that recycles a detergent solution.
2. Background Art
Soil having a high concentration of oil has been cleaned by vaporization or incineration. These thermal processes, however, require an excessive amount of heat when the concentration of oil is low, especially when the concentration of oil is low compared to moisture content of the soil.
Soil washing systems have been devised, but in general they have had a relatively low-volume through-put and have involved excessive waste-water treatment, rendering the process uneconomical or impractical. Soil washing systems have also been limited at certain sites by the presence of a high concentration of silt or clay in the soil to be washed.
An overview of soil remediation techniques is found in the EPA handbook entitled "Remediation of Contaminated Sediments," EPA/625/6-91/028 (April 1991). On page 32 of this handbook, it is said seventeen full-scale commercial soil washing plants are currently in operation in Europe, and these plants are capable of handling from 10-130 tons of sediment per hour. The EPA has found that the effectiveness of the European soil washing plants may be limited at certain sites by the size of particles they rejected (particle classification is an early step in the European soil washing process.)
Further details regarding the background art in soil washing is shown on pages 9-3 to 9-7 of the EPA "Contaminated Sediments Seminar--Speaker Slide Copies," CERI-91-19, May 1991. As shown on page 9-6, an aqueous soil washing process includes soil preparation for removing oversize rejects, soil washing, rinsing, size separation to separate clean soil from sludge and contaminated fines, waste-water treatment of "blowdown" water, and recycling of some of the treated water. The operation of a cyclone for particle separation is shown on page 7-7.